It... didn't work? I tested it at the time and I just tested it now (to reassure I actually did test it back then), the objective was to make it so that 1/10 of HP recovered becomes 1/X'th of HP recovered, wasn't it? What happened when you tried it, out of curiosity? That sort of shakes my confidence a little to have it work for me, but not for others.
A fix for 1/3 current HP is the same case as my original formula posted above... changing This...
$03/DD6E A2 03 00 LDX #$0003 A:0000 X:0001 Y:0000 P:envMxdiZc - Load 03 into X (/3. How much % of HP to heal.)
$03/DD71 8E 47 39 STX $3947 [$7E:3947] A:0000 X:0003 Y:0000 P:envMxdizc - Store X in 7E3947.
To this...
$03/DD6E AD 9D 28 LDA $289D [$7E:289D] A:000B X:0058 Y:FFFF P:envMxdizc
$03/DD71 8D 47 39 STA $3947 [$7E:3947] A:0002 X:0058 Y:FFFF P:envMxdizc