Hello,
I once read on a website that a vagina is small enough to hold a tampon and large enough to squeeze out a baby the size of a melon. So I doubt that his penis is 'too small'. Telling him this would not be a good idea. It would be like him telling you that you're breasts are too small or your vagina too saggy. You could always try different positions that will allow more depth during penetration, such as doggy (him taking you from behind), putting your legs over his shoulders etc or trying things like putting a pillow under your bum to lift up your pelvis, or putting the pillow under your pelvis if he is doing you from behind or squeeze your legs together as he enters you. For more tips to make him seem longer, thicker and add more depth, you can email me if you like.
Dani x