Jem'Hadar?

[Warspite]

Why not just have them all in one place? So the Feds can't pass.

For the same reason you don't put all your eggs in one basket. If something went wrong, you loose everything. If the mines were all in one area, logic dictates that the enemy could bypass them alltogether. It'd be like swerving around a pothole in the road. Then there' the risk of setting them all off when one of the mines takes out an enemy. That would be BAD since it reduces the effective defense dramatically. Spreading them out to make a perimeter would be FAR more effective.

Mines are used to steer an enemy into predictable (and lethal) avenues of approach, or to defend less important areas. The separation can be calculated, so one explosion wouldn't blow up the nearest mines.

[TheDarkling]

The thing is however the Feds were defending so a standard mine field is of no use, stopping your enemy for moving is all very well and good but it their mission objectives don't include moving you aren't going to affcet them.

That being said the subspace mines are dumb anyway, why didn't Jem Hadar simply cause the mines to flood the compound and kill everyone there thus retaking the comm station.

[The Nomad]

Note that cloaked JH can be easily picked up by a tricorder, as we saw in "Rocks and Shoals", and you should be able to see them on infrared.

At point blank range ( Garak and Nog IIRC ) , weakened ( KW lack ) JHs.
At long range, unshrouded JH.
Not that simple.

Anyway, they can't be shrouded from the whole spectrum, unless they use sounds or odours for perception - ( well, they need to breath, don't they, so their shroud is surely only EM, not particle-based ), or a treknobabble solution - neutrino sensors, shift-phased polaronic beams or whatever meaningless polysyllabic solution.
Of course they might have some problems with waste heat - unless they have special organs or organites to "store" it for long shrouding.

[The Nomad]

And apparently houdinis can move within your ennemy's positions without being intercepted, thus making them more efficient than some here believe. At least, psychologically.