I'm sorry I have not reached correct answer yet in spite of long thinking.
I tried reconstructing your map data but it was no go.
However, I can show you my interim progress.
Could you download and refer to [93334X4S]?
Please download it asap because I'll keep it on the cloud server temporarily.
Please note that you need additional purchase DLC (Advanced Sound Processing Unit) to play this game.
Current key is NEDX43CJ and file name of this game is HNZVTS.
ACLS:HP=20:RF=0
FOR I=0 TO 19
VSYNC 1:GFILL 80+I*4,8,80+I*4+2,15,#YELLOW
NEXT I
LOCATE 2,3:?"Pressing A button gives you 7 damages."
WHILE TRUE
VSYNC 1
IF(BUTTON(2)AND #A)!=0 && RF<=0 THEN RF=7
IF RF>0 THEN
DEC HP,(HP>0):DEC RF
GFILL 80+HP*4,8,80+HP*4+2,15,#RED
ENDIF
WEND
One thing I can say for sure is that distance ratio is equal to size ratio. In other words, if A is twice as far as B, A looks like half as large as B. We should grasp positional relation between sprites and your viewpoint to set parameter for SPSCALE correctly.
Multiplayer has low priority for me because I have no experience for wireless communication on 3DS. I hope you'll not take it amiss.