chances of getting a bid to a mid tier house

Long story short, I am a sophomore who has been attending events for what seem to be considered mid tier fraternities (SAE, Delt, etc). I'm pretty introverted but have been going around and talking to a lot of the guys. I've just been making small talk with a lot of the guys, and most of the people who I talked to for significant amounts of time seem to remember me and say hello or whatever when I see them around campus or pass by them at an event. I have not been invited to go to any invite only events yet, and do not know if that bodes poorly for my chance of getting a bid to any of the fraternities I have visited. Should I be concerned, or should I just keep going to events, meeting the brothers, and praying that i'm cool/interesting enough to be considered?