We only open ours if extremely hot and sunny where it's just too uncomfortable without some shade relief. That's maybe a couple times a year. Today just may be one of those days. 100 plus with the heat index, in the forecast.
When it's just me out fishing I don't bother to open it but when the family is on board we open it. We find that on hot days the shade it provides makes it much more comfortable for those who don't like to jump in the lake to cool off.
Our bimini is normally down on the trailering legs and not up in the radar position as we have to go under a bridge to get to open water from our marina. Once out on the water it all depends on temp and if we have guests on board as to if we open the bimini. I'd guess it's open about 30-40% of the time we are on the water.
Last weekend it was open most of the day as we had events in the harbor that had us docked for most of the morning (10-3pm). We like the fact you can be out on the water with the bimini for shade even on hot days and still enjoy boating without feeling like you are being cooked alive.
I haven't had to do this to mine but it looks like you have the same adjustable knob on the forward-most support. Sliding the whole arm up closer to the canvas should pull the bimini down more and provide more tension. Mark where it's at now so you know where you started from. If that doesn't work it would also be really easy to shorten the rear support, it's just attached with screws. I would remove the plastic insert and lop off a small amount of tube, drill a new hole for the screw, and test fit. Repeat as necessary.
My double stays up all the time. I only have to tow about 2 miles from my garage to the ramp. Should I travel to Mead or Powell in the future then I'll drop them down for the long tow. Right now, I boat exclusively on Havasu and having both bimini's up is a must.
I would say my Bimini is used more than anyone's. We keep the boat on a lift so it goes into the trailering position every time we come into the lift. Having a little one we open it all up as soon as we back out of the lift. So my boot comes on and off daily.
My double bimini has been up 100% since we picked it up from the dealer. Even with it up, if one wants to get some sun, there is plenty of sun up towards the bow. Did I mention it gets a bit warm here?