Could it be because we often have only one encounter per day, though it's invariably at (PC levels + 3) or more?
Seconded.As you have figured, your decision to only run one fight per day is what causes your issue along with the fact that you are throwing n+3 encounters at them. If you want to create deadly combats for a fully rested party, you need to push the combats to n+4, n+5, possibly even n+6 depending on level and skill of your group.
Another way to threaten them more is to have monsters focus on one character at a time (within reason of course). Preferably not the defender.
You could always throw the pre-eratta daggertooth drake swarm.
If no one's scared, dead or whatever it is you want to achieve then the encounter doesn't stop there, a door opens and in walks... and then... and then... make them run away a couple of times, that makes me smile.
To clarify, what I didn't like was to have my stunned PC dropped into the well with a move action and with no roll - i.e. essentially for free as far as the action economy and any other form of resources were concerned. If you'd action pointed and used that to drop Hoka down the well I wouldn't have minded anything like as much. If you'd spread it out over two turns that wouldn't have been half as annoying (i.e. grabbed and stunned Hoka turn 1, and pulled him in turn 2 giving him a chance to save or escape) that would have been better. If you'd done it in one turn using an action point, hell, it's an action point - they should be scary.
But the way you had it set up was esentially roll to hit on standard, roll to hit on minor, automatic kill on move - all within the space of one turn and as SOP from a monster very unlikely to miss (higher levelled elite soldier IIRC). It was like the old 3.5 Save or Die spells in a game set up to deliberately avoid Save or Dies (OK, so it was two easy rolls rather than one hard one to almost entirely neutralise a PC for the remainder of the encounter - and kill him if we lost).
But the way you had it set up was esentially roll to hit on standard, roll to hit on minor, automatic kill on move - all within the space of one turn and as SOP from a monster very unlikely to miss (higher levelled elite soldier IIRC). It was like the old 3.5 Save or Die spells in a game set up to deliberately avoid Save or Dies (OK, so it was two easy rolls rather than one hard one to almost entirely neutralise a PC for the remainder of the encounter - and kill him if we lost).
And four of them in one encounter facing 33(?) orcs. To be fair, I enjoy the higher difficulty level as long as I think there's something I can do about it.
Killing players treads perilously close to going to jail.
Killing characters? Totally different.
An unconscious character in the auto-attack area of a swarm is also harsh. I almost died from that.

(Dungeons & Dragons)
Rulebook featuring "high magic" options, including a host of new spells.