Hello cccrunner,
That is a great personallity trait to develop. I used to struggle with groups alot aswell and came across as quite distant. I don't know what you are doing right or what you are doing wrong, but I can go over some common issues.
There are alot of aspects to focus on, but one huge factor is openness. You cannot judge people for their actions, decisions, ideals... ect. Now that doesn't mean you can't have standards or expectations, but just remember, each person has their own standards and expectations and they have them because of their experiences. If you are accepting of everyone, they will be alot more likely to open up around you, and you will not have to pretend in order to fit in.
Another big one is to smile. If you don't smile, people will either think you are an unhappy person, or you don't like them. Be careful not to smile too much, because that could mean a number of things, but none of them are what you want. Some people don't trust someone who smiles all the time, because they think they are fake and trying to fool people for one reason or another. It might make you come across as akward or nervous, or people will assume you aren't socially aware of the situation and that places you at a lower value. I hope that didn't scare you too much! It still is very important to smile; just make sure it's at the right time.
Also, if you can crack a good joke here or there or come up with a clever riposte, it is amazing how quickly a group will accept you. I'm still trying to figure out how to master wit myself, so I can't explain how to learn it. One thing to keep in mind, don't joke too much or you will end up labeled the group entertainer and that will limit your sexiness. And if you keep joking around to an even further extent, the group will get annoyed and reject you. Just use humor and with here and there to interest people.
Something very important for coming across as warm in a one-on-one setting, is to actively listen. I used to think I was a good listener when I was a little kid, because I was too shy to talk, so I only ever listened. But not talking really just makes you an observer, and will either make you invisible, or will scare people away. Nobody wants to be observed like some science experiment. To be a good listener, you have to stay engaged and ask interesting questions. Just be sure you relate aswell as ask. If you only ask questions, it will seem like an interrogation. Be sure to relate what they say to your own thoughts/experience, but don't go into much detail. Keep the conversation focused on them. As long as you keep a good balance between asking and relating, you will be quite a warm, likeable person.
Now that last paragraph is all good and well for conversing with one or two people, but you want to be skilled in groups. Groups used to frustrate me aswell. I can remember being fairly experienced in a one-on-one conversation, but as soon as there was a group, I would close up and be silent. It seemed impossible to think of anything good to say. What made it even more frustrating is that asking questions and relating didn't seem to work. Now I am still not as experienced with group interaction (or any social situation for that matter) as many of the members of this board, but I can tell you what has worked for me.
The reason asking questions and relating didn't work in groups is because it caused the focus of the whole group to shift onto who I was talking to, and made it very personal. Most groups are impersonal. What you have to do is ask a question, but keep everyone else in the group engaged. Look over at others and ask there opinion. Another thing is that you have alot more people, and they all want to talk. This means there is often twice as much or more that is trying to be said. You really have to speak up to be heard. Especially if the group is not made up of socially aware people. Try not to bring up any inside jokes, or experiences you had with only one other member. If you do bring up that type of experience, make it engaging and try to involve other people. Once you start figuring things out, you will start to realize that groups are looking to you to lead them. Once that is the case, everything seems so much easier, because you can regulate who is talking and make sure the topics are interesting.
I could say more, but that was already such a long-winded answer, I don't want to make it longer. I hope it helped you. If not, Chase does a far better job of breaking it down here
https://www.girlschase.com/content/tactics-tuesdays-how-be-warm-person
I didn't have time to go over magnetism because I have to go to work now. If you would like, I can go over it when I have time.
Good luck!
-Mark