Prop problem or something else????

Using my recently purchased nearly new 9.9 4-stroke Mercury kicker that is mounted on the port side, next to my 100hp Mercury, I cannot turn into the wind that is coming from starboard to port when the wind is above 8mph. I troll on Lake Michigan at 2.5mph (which is at about 500-700 rpm), and the only way I can make a slow turn or fast turn into the wind when the wind is coming from starboard to port is to increase speed to 4+mph (1,200 rpm or so), which defeats the purpose of trolling at 2.5mph, since turns with downriggers need to be gradual. My prior 4hp 2-stroke worked OK, but was always above 1/2 throttle (sometimes 3/4) just to maintain 2.5mph, and could not navigate wind and waves. The 9.9 does this fine, except it will not push the bow into the wind when the wind is coming from the kicker's side of the boat.

I need some insights into the principles involved to help me figure this out.

I think the problem rests in one of 4 areas, or a combination. 1) the steering bar connecting the 9.9 and 100 is further out from the 9.9 than it is from the 100, thus the bar is not parallel between the motors. Thus, the angle causes the 9.9 to turn less than the 100 when the steering wheel is turned all the way in either direction. I plan to try to correct this so the steering bar is parallel with the 100hp steering rod, but some fabrication will be needed. 2) At 2.5mph, the engine is barely above idle, about 500-700 rpm. It would seem a different prop would allow the motor to run at higher revs and thus make more cuts in the water, thus facilitate turning without needing to increase the engine rpm. Is this correct? If so, a prop change may be in order. I believe the stock prop is 9 x 8.5, but will check to make sure. We have a superb prop man locally who can direct me to what I may need. I don't want speed, just thrust for turning, and an occasional emergency motor backup in case the 100hp refuses to start when 2+ miles out in Lake Michigan. 3) the 9.9 is a long shaft. The boat is a very deep V aluminum (2,000-2,500lbs with 100hp, fuel, supplies, and up to 3 men). A long shaft seems about right as the cavitation plate is in about the right spot, just a little low. A standard (short) shaft works too, but barely. Could the longer shaft be a problem? Should I raise the motor 1-2"? 4) the very deep V acts like a keel which is harder to turn in the wind. I cannot do anything about that, but it may magnify any symptoms. The kicker is attached to the stern at the same spot where the 4hp was attached so that location should not be causing the problem.

I've checked everything I can check. The kicker is all the way down in the water. There is nothing blocking the propeller thrust.

Is there something else I'm not considering? Insights and thoughts from any of you experts out there would be greatly appreciated.