How do you make upgradable ores-gen?

[BrownMee]

Im not sure how to create a skyblock cobble gen . Can be also upgradable. Can anyone help me with this?
[doublepost=1528905617,1528902032][/doublepost]on break:
if event-block is cobblestone:
loop blocks in radius 1 around the event-block:
if loop-block is lava:
send "s"
wait 1 ticks
set block at event-block to coal ore

sometimes work but sometimes doesn't

 

[DieHollander_]

on form:
    if id of block is 4:
        set block to coal ore

 

[BrownMee]

on form:
    if id of block is 4:
        set block to coal ore

What if making it upgradable? This is what I came up

on block form:
    event-block is 4:0:
        loop players in radius 1 around the event-block:
            wait 1 ticks
            {coal1.%loop-players%} is true:
                chance of 2.0%:
                    set block at event-block to coal ore
                    stop

But it's not efficient as it loops all players in server so lets say:

Player A has the {coal1.%loop-players%} variable
Player B has the {coal3.%loop-players%} variable

It will form coal ore chance higher since it loops all players.

 

[DieHollander_]

There's no other way to do it. If you are using a skyblock plugin you could try get the owner of the island.