long time no post, so it's nice to see all the activity still on the boards!

i was wondering, my indo's are large-ish (either a large medium, or a smallish large), and i've had them since around the new year.
for as long as i've had them, i've not seen them burrow to molt. they are active at night, and i've seen them eating.
sometimes i see them climbing around the 'tat, so is it a factor of their size that reflects their lack of molt?
my straw's (2 of them) have molted twice with me, and my E's have molted multiple times, so i don't believe it's a factor of the substrate, which is 6" deep, and a mix of EE and high desert sand.
humidity ranges between 85-90%, and the temperature hovers right around 80 degrees.
thoughts?