Engine question

[Driftwood]

I'm new to nitro buggies but I am now hooked on them! So much faster in my garden than my old Tamiya Dirt Thrasher! Too fast actually! Anyway, being new to nitro power I damaged the pull starter during my attempts to start the damn thing. Hopefully I haven't damaged the engine too, as it may have flooded. Have now worked out how to start it, but during the repair I had to remove the exhaust system. Whilst it was off I had a look down the exhaust port and noticed that the bottom edge of the hole in the liner is higher than the bottom edge of the port by a good few mm and that the piston crown at b.d.c. is lower than the bottom edge of the hole in the liner by about the same amount. Is this normal? Experience of 2 strokes in 'bikes says not and that it could restrict power, but rc motors could be completely different especially as they don't use reed vaves. Or an ignition system.
The motor in question is a Force 21 fitted to a G.V. Rex-X. Are they any good? Any recommended modifications?
More questions to follow, no doubt...