My Tarantula's abdomen's size

I've had my 3 yr. old male Chilean Rose Hair "Venom" for almost 2 mos. now & his abdomen I've noticed is the size of a grape, not too small or anything, a nice rounded size. I'd assume since he's still growing & Chilean Rose's don't reach full maturity till about 4, that his abdomen will also get just a little bigger too if I'm right? I'm still feeding my T 4 crickets a week. Should I increase that a little to help w/ his growth or is 4 crickets good for now? I've also been keeping the heating lamp light on real (low) & the new heating pad I have on the outside of the tank glass in the back & I've noticed the humidity's been staying in the low to almost mid 60% range & the temp's have been around the low to high 70's, sometimes in the low 80's a few times! I remember u telling me to not use a heating lamp cause it'll dry out my Chilean Rose, but it seems since I've been keeping it on really low, the humidity/temp's have gotten better. I also did spray the soil w/ the water mist bottle today (2-3 quick squirts) & I made sure I didn't spray anywhere near my T!

If the abdomen is like a grape I would feed him a little bit more.