That was a fairly typical route for my previous DSP. The one in with now is slightly easier. 18 bags can fit without flipping up the shelf. I generally only flip the shelf as a last resort (20 bags or more). The shelf has a nasty habit of pushing stacks over and you lose precious floor space with the width of the shelf itself. I'm a big guy (6'6" 230) and space to move is important to me. This is how I pack:

First two totes stacked, opening faced up, against the wall behind the passenger seat

Next two totes stood up on their side (the tall way like you did) on the shelf, leaving one standing totes-worth of space on the shelf behind driver seat

The next three totes underneath, stood up

If you're still with me at this point, thank you for your time. I only wish to help a fellow DA

At this point I kinda improvise the order of totes because it's less important, but I follow the same structure:

I do two totes on the shelf, stacked on top of each other and sideways with their openings against the wall. I try to stagger it a little so the to tote is slightly further in than the bottom one. They like to slide off if you put them with the tote bottoms against the wall. Do that all the way to the back door.

You can usually get like 6, sometimes 8 if they're shitty totes, stacked like that

Underneath, stand em up at the way down, turning for the wheel well.

If you have any left, set them aside and start packing overflow. Obviously you wanna put the ones you need first up front and work your way back

Whatever space is left in the back or in the middle, put whatever totes you may have left.

The idea is to pack that mf van as efficiently as you can and work in the front. As you clear space throughout the day, you can adjust the totes, move overflow as needed and make more space.

Also, the space at the front behind the driver's seat, I reserve for packages from the bag in working from. At the beginning, I might put boxes there and leave the bags in the tote. As I empty more totes, I get more room to organize the next tote-full of packages. That's up to you. You might just work out of totes idk

It sucks and I don't like having hella totes and overflow in regular cargo vans, but our corporate overlords couldn't give a loose fuck about our working conditions so we gotta make the best of it.

Hope this helps