I agree. A wider cone angle is better onLM. My old Si-Tex paper graph with a 50 degree transducer marked like no other.
I think when you are referring to a 4” and a 7” you might be referring to screen size. Cone angle and area of bottom marked has to do with transducer(TD) frequency not screen size. The exception being that smaller screens can’t really operate split screens well so they more often have a single more general use transducer. When you get into the larger screens you can get dual frequency TD’s and operate a split screen to see both. I am a Lowrance guy. One frequency of my dual frequency TD I had a purchase choice of 50/200kHz or 83/200kHz. When in use you can set it to 50 or 200kHz. 50kHz has more bottom area marked. If using 83/200kHz the 83 marks more bottom than the 200 but not as much as 50 would. So you have a purchase choice then a setup choice. The second band that comes withe a unit with the dual band feature is 455/800kHz. That doesn’t mark fish that well but has incredible detail of inanimate objects. Like in LM the 83/200 will mark a rock pile as a blob which might be a school of fish, a blob of weeds or a tree top. The 455/800 will show you each rock and the split screen will show you the fish on the 50/200kHz or the 83/200kHz. The 455/800kHz is amazing. You can see so much detail. Like branches on a tree. You can tell what species of weed are down in 12 fow. It will tell you where the spot on the spot is. Like weeds on the edge of a drop. A wall of weeds not so good. When you find 10’ of weeds that turns into 8 then 5 then 3,3,2,2,2 then 1,1,1 that’s it. I call it the 3,2,1 not a wall. Pull your harnesses over that spot. That is brought to you by 455/800kHz.
WhenI am on LM I keep charting on because there are some some charted differences that seem to correlated to fish especially lake trout. You need to zoom in to get the detail. Put plugs on the bottom in those spots. You will get Lakers. Then setup for single split and put away 455/800kHz. There is no detail to be marked unless at the rock piles by the project. Change 83/200kHz to 83kHz. Now you have a bigger picture and maximum bottom area marked. As soon as you come back into Pentwater changes need to be made again.
That is why in my first note I mentioned having it close enough to setup and change. If it’s too far away you leave it on what it was on and you could do better. Knowing how to change it quickly is why I recommended YouTube to learn and saving screen shots for quick reference in the boat. Get a good machine. Spend the money. Learn, practice, repeat = fish in the box.