What is your suggestion?

I'm currently developing a datapack that uses pehkui a lot. and I'm often finding myself having to create complex solutions to get around a few base game integrations features that are missing.

Selector variables

• IS tag @A[pehkui.scale=1] - added
• IS NOT @A[pehkui.scale=!1] - missing
• Greater than @A[pehkui.scale=1..] - missing
• Less than @A[pehkui.scale=..1] - missing
• Between x&y @A[pehkui.scale=1.2] - missing

Scoreboards

Scoreboards that are directly linked to a player's size. this would be a great way around selector variables because the scoreboard would inherit the default selector variables

/scoreboard objectives add BaseSize pehkui:Base

I'm using the latest Pehkui version and I can say that "greater than", "less than" and "between x&y" already exist.
And your suggestion about scoreboards is impossible because scoreboards uses integer values and player size is a float value. You can use something like
/execute as @a store result score @s scale run data get entity @s "pehkui:scale_data_types"."pehkui:base".scale
but it will only show you integer values e.g. 0 if it's anything between 0 and 1, 1 if it's anything between 1 and 2. This can't be changed because of the way how Minecraft works.

Scoreboards are 100% possible you can convert a float to an integer, you just need to round to the nearest predetermined float. say sets of 0.25
1.75=3 | 1.5=2 | 1.25=1 | 1=0 | 0.75=-1 | 0.5=-2 | 0.25=-1

Ideally, you would probably round to the nearest pixel. in this example p=pixel s=scale/size
if s=1 p=32 score is 32, if s=0.5 p=16, if s=0.03125 p=1
If s=0.03125 p=1 then s=0.0625 = p=2 0.046875 is the magic halfway point

if i could use the pehkui variable to test between variables I could do this within the restrictions of commands. i see no reason why it couldnt be done within the mod. If there is something I've overlooked or done incorrectly please, let me know @ImSpaceLover

As for /execute as @a store that's great. and if you added an "unless size=1" filter you could tell if a player was shrunk, but you still can't tell the difference between someone that is half or quarter-sized

your idea with storing floats like this is good but I just remembered /data get entity has scale for /execute store so you can divide stored number to get your original scale. For example I used
execute unless entity @p[pehkui.scale=1] as @a store result score @s scale run data get entity @s "pehkui:scale_data_types"."pehkui:base".scale 1000000
to store my scale in a scoreboard and then used
execute as @e[type=wolf] store result entity @s "pehkui:scale_data_types"."pehkui:base".scale float 0.000001 run scoreboard players get @p scale
to make every wolf copy my scale. I used only 1 million scoreboard scale so when my own scale is smaller than this every wolf, obviously, becomes 0 sized. You can use more to make scaling more accurate but I think this is enough.
Also I just used
scale reset @e[pehkui.scale=4..16] in a command block and it worked fine

the wolf scaling is an interesting idea. i hadn't considered pets, i really like that idea, and id love to try and make it multiplayer friendly, ill have to figure out a way to make it only apply to pets you own. I need to play around with execute more because there is a lot i dont know about how it works.

Regarding scale reset @e[pehkui.scale=4..16] reset is the only command that works with those parameters, but that gives me another idea, i just assumed that none of them work, but if reset works, i can convert the reset command into others based on my size scoreboard, thanks for that

I used wolf scaling just as an example, I hadn't considered scaling pets either. I think it's possible to make it multiplayer-friendly by matching wolves' (and other pets') Owner NBT tag and players' UUID NBT tag and scaling them only if they match

Also, do you have a discord account or something? I think our conversation is a bit off-topic now, would be nice to continue it in DMs