Two ways of reeving the mainsheet in this gross fine mainsheet system are shown. The more obvious way to do it is shown on the right. The problem is that the lines hit each other, the fine control blocks hit the main sheet, and in general it has problems.

The other way rotates the main dual block by 90 degrees and has no such interference issues. It also opens up a large space for the fine tackle so that it does not rub on the mainsheet.

It is often the case that crossing blocks so that the lower block feeds the sheet from one of the upper sheives to the other rather than following back to the same sheave is the better way to rig blocks.

In general, reeveing with crossed blocks is often a cleaner lower friction way to rig your blocks. Above is shown the simple case of a pair of double blocks such as the setup I use on the cunningham on Papoose.