Rug sizing help please

[Clannad48]

I need to buy a new indoor rug for our horse a 17.1hh Dutch warmblood mare. She takes a 6'9 outdoor and the last time we bought an indoor one it fitted - however, now she has grown it looks like a mini skirt on her. Does anyone know of a rug that has nice long sides that will keep her covered.

Hoping someone will be able to give me some advice.

 

[painted ponies]

Mastas are normally a little longer, I also have 2 amerigo's 1 6'6 and another 6'9 the 6'9 one seems considerably larger than 3', they were both bought second hand so maybe the larger is newer?