The longer tail moment is the culprit. My 4* 60 doesn't seem to be so touchy on CG, as some other planes. Balance it a tad nose heavy, if it flys well...you're done. If it lands 'hot', add a bit of weight to the tail, or adjust your battery and/or RX. The 4* is a floater, and it doesn't seem to mind balancing a tad behind the spar.

That 4* 40 should land at a quick walk...say 5-7 MPH.