Locus Mine Support's detonate range limit applies to your mouse position for sequenced detonation.

When using Locus Mine Support, the mines are support to detonate in sequence like other mine skills when using Detonate Mines.

This appears to only be the case if your cursor is within the noted 3 metres distance from your character, found on the gem like this:
"Mines from supported skills can't be detonated while withing 3 metres of you"

If your cursor is outside of this range as well, Detonate Mines will only detonate 1/3 of the thrown mines, whilst if the cursor is within range, the detonation will act correctly like other mine skills and detonate them all in sequence.
Considering you have to throw the mines out further than the noted range, your mines will never correctly detonate whilst your cursor is at the location you just threw the mines at.

It is almost impossible to flick your mouse back to your character instantly during regular gameplay where you have to keep moving and makes for a clunkier experience than is intended. Whilst also effectively lowering your damage and making it so you hit the mine cap instantly without being able to ever detonate all of them.