It doesn't matter whether the panel is vertical or horizontal.
Ahh but I think it does matter and that's what I am very badly trying to explain, the panel is 10 cells x 6 cells. Each string of 10 cells is connected in series and then adjacent strings of 10 cells are connected in series with a shading diode across the other end so there are 3 shading diodes in total each handling 20 cells.
Now imagine as is currently the case the shading occurs evenly across each set of 20 cells then the shading diodes do nothing and the panel output current cannot rise above that of the shaded cells. However if one group of 20 cells is shaded whilst the other two groups of 20 are not then the shading diode will conduct across the shaded group allowing the output current of the panel to equal the unshaded cells.
So for the situation that I have where the shading is a horizontal band climbing up the array landscape panel orientation would definitely give higher output.
However I have to agree shifting the whole lot higher up the roof would be very effective except I am not as agile as I was and it would make cleaning them with a sponge on the end of a garden cane as I presently do impossible. I am in a windy farming area and some soil gets deposited on them in the summer.
I have a near neighbor with a similar sized roof with two rows of 8 panels in portrait (~4Kw+) and I see the lower row often in part horizontal shade and I wonder if the system performance would have been better if they were in landscape, but potentially the downside is more fixing hardware (rails, mounts etc) and that may be why I see them always portrait. As for me I simply copied everybody else without thinking about it
BTW this site is annoying timing you out when you take a while to write a reply!