I've gotten every part I have ever made right on the 1st attempt once I figured out not to let the printer fit the parts to the page. A lot of people use the height method so their pieces are 1:1 game accurate... but not everyone is the same size, some people have gorilla arms, or giraffe legs and some even have over sized heads or the dreaded beer belly... The parts are displayed in their exact 3-D dimensions if you look to the specify scale page. Depending on the part you just have to add extra to accommodate padding and extra resin. The forearms can be difficult to size right, I sized mine 2 slightly different sizes. 1st one is game accurate the part is the entire length of your forearm bone, from the base of your wrist to the edge of your elbow and it fits me perfectly, the wrist hole is perfect, the other is 1 centimeter shorter and I had to carve a lot into the wrist hole for my mitts to get through it.
The trick is to actually measure the dimensions of yourself for the part you are trying to wear.
For the torso, it depends if you are a scrawny person, if you are scrawny you will want it smaller than it should be to look good on you. For myself I measured myself from the edge of my shoulder bone, feel the top of your shoulder, the top of the cup on top of your shoulder. measure yourself from the edge of it on your left side to the edge of yourself on your right side. You will have a little meat on your arms sticking out, but that's totalyl normal, don't include your biceps into the measurement, they get their own armor piece to cover them. if you do figure them in, you will have problems raising your arms up very high when you are all suited up.
Measure yourself from your front to back widest spot. For a lot of people its from tour stomach to your back (may need help as this part is difficult) then measure yourself from a few inches above your shoulders down to midway between your belly button and your soloplex (bone in the middle of your chest that sticks down).
You should match the width measurement 1st and see how the rest of the armor dimensions are when they are displayed. odds are they will be just fine. If you are wider in the mid section, like me and several other people are, you will have to split the side parts off and turn it into 4 pieces. if the side parts don't touch the front and the back parts of the armor, don't worry about it, I attached mine with a very large piece of Velcro. I attached 2 rivets to both side pieces to make sure the Velcro wouldn't come off, then left a foot and a half of Velcro to attach it to the front and back pieces. You could easily get by with less, but I wanted mine to be expandable to fit just about anyone.
Now if you do split the armor, the best method and probably the easiest method for joining them back together when you are done is using a 2 foot long strip of industrial Velcro. Using Velcro, your chest pieces attaches very quickly and holds very well. I would suggest covering the area under where the sticky part of the Velcro will stick to the chest piece with painters tape as Velcro sticks to dried resin like super glue and it doesn't always stick very good to painted surfaces.
Before you split your armor, if you do go that route, make sure you apply resin to the outside AND the inside of your armor piece the best you can so it won't warp.
I'm sure that's more info than you were looking for, good luck on it