I have a Kohler toilet in my bathroom with these numbers in the tank

T 39
K4519
20399
3 1

What is this model toilet's reputation in regards to flushing solid waste? I'm considering replacing it because it seems to get clogged fairly regularly by one adult member of the family and one who is not even a teenager yet. If this toilet is supposed to be good a handling solids, I'll go ahead and do some of the things suggested on some of the other threads I've read on this forum before resorting to replacing it.

Also, can someone offer some guidance on the proper water level. The word "waterline" is inked in the tank just below a small ledge that runs around the circumference of the tank. Is the proper water level supposed to be even with that ledge? My water level is about 3/8" below the ledge, maybe that could be the cause of the clogging? I do not have an owner's guide, and have been unable to locate one on the web to verify the proper water level.

Any ideas would be appreciated