Get used to baitfishers outfishing you. That's just the way it is.
In "a passion for steelhead" I believe Dec calls it a "pullback mend."
Correct me if I'm wrong.
Anyhow, I'm not really a fan of casting 90 degrees. Below I'll make those reasons clear.
For the most part, I'll just do the big upstream mend. Cast slightly down stream and well over the area you're trying to get your fly to drop in and as soon as it hits the water, pull waaaaaay back. Your line will now be parallel with the flow and will give you a few seconds of complete slack for the fly/tip to sink in. If you want it to go deeper, have some extra running line ready to be fed into it. That will give you another few seconds of slack.
I find this to be "better" than the 90 degree method for these reasons:
1) your fly "dead drifts" but you don't lose "touch" with it. I find with the 90 method, there is a period where you have so much slack in your line that if a fish grabbed it, you'd not be able to feel it. Plus fish like the dead drift especially if you lay your line into a slot.
2) when you do the mend AFTER it's already began to sink, you will pull your fly up in the water column. With the pullback method, once it starts to sink you leave it alone.
3) people can't tell you that you're flossing
But seriously...I've seen a few vids of speycasters with T17 or leadcore and I feel that where they took the fly in the "swing" and the position of the line, the fish could have very well have been flossed. But to each their own.
That being said, maybe I just do the 90 deg method incorrectly. This is just what I have learned from swinging the rivers here for bulls. You need to get down fast in very deep pools.
Other things to consider for gaining depth: smaller diameter tippet and rapala knots.
Just my opinion and what I find that works for me.