Interesting... They are an on-ear headphone so in theory your ears should come nowhere near the grill. Sounds like you are using them more like an over ear with your smaller sized ears.
The M80 has much smaller pads and might act more like a true on-ear headphone for you. You will notice a significantly lesser bass presence with the M80 vs the MS400.
Sorry I say interesting above because I found the MS400 to be the most comfy on-ear headphone I have ever owned/used.
You could consider a portable over ear for more comfort. I really liked the UE6000 in this regard. They have a similar bass quantity as your MS400 but with more refined highs IMO.
Other on ear suggestions:
B&W P5 (have a different type of pad all together, I found them to sound very good indeed with good comfort for the short time I had to try them)