The LFG random finder is really a mysterious tool.
On my mage, for example, i've got H Oculus maybe.. once? twice? I've got H TOC, FOS, POS, HOR maybe 3-4 times max! Yet, i get H DTK or H HOS like 75 times.
BUT, on my warrior, it really IS random, i get H Oculus & H TOC, FOS, POS, HOR as much as every other heroics. Same thing for my healers alt.
Why is my mage having such a hard time getting those heroics, i have no clue. Must be something about DPS selecting those dungeons as specific for their 232 epics or something and they have priority over DPS using the random option.