The boot floor has 2 positions. You can use the lower as you are, or use the upper as Dodger is. Just pull the floor out and slide it onto the upper supports that you pointed out to use the higher setting.
I have spacesaver spare and the floor still fits nicely on the lower setting.
I use lower setting when filling the boot e.g. holiday, and the higher for day to day to use, e.g. shopping as it is easier to slide things in and out.
When you have it on the lower setting to fully open the underfloor space you do have to slide the floor towards the rear of the car a bit as you lift it to prevent it catching on the upper supports as you have pointed out.
When I considered buying the MG spacer saver, I did not really want to loose the facility to use both levels of the boot floor cover.
I like to use the extra space in the boot with the board on the lower setting.
I found that when using the MG space saver you CAN set the floor level in the lower setting.
If you use a full size spare wheel, you will loose the lower setting.
I don’t see the need to carry the MG inflation kit anymore ?.
I just carry a can of Holts tyre repair foam in a can, just for belt & braces ?!.
I coil my type 2 public charging cable around the outside of the space saver wheel ( not used a lot ) and therefore the boot is always neat and tidy.
The warning triangle sits behind the space saver, below the boot cover board also.
So, no loss in space in the boot and everything is packed away.
The boot cover board is then protected by the MG interior protective boot floor liner.
It came in a “Interior Protection Pack” that included the following items.
Front and rear tailored mats, boot liner and front and rear mud flaps.
I think it was about £130.00 at the time.
Which I though it was a reasonable.
The MG space saver kit was the same price, but I believe it has increased a LOT in price now due to popularity.