Let's try this ...

I order the following:

1 x Product 1 (flat rate)
what is my shipping?

2 x Product 1 (flat rate)
what is my shipping?

1 x Product 1 (flat rate)
1 x Product 2 (flat rate)
what is my shipping?

1 x Product 1 (flat rate)
3 x Product 2 (flat rate)
what is my shipping?

Now I order something that is NOT a flat rate product ...

1 x Product 4 (Normal weight) UPS $5.95
what is my shipping?

1 x Product 4 (Normal weight) UPS $5.95
1 x Product 1 (flat rate)
what is my shipping?

1 x Product 4 (Normal weight) UPS $5.95
2 x Product 1 (flat rate)
what is my shipping?

1 x Product 4 (Normal weight) UPS $5.95
1 x Product 1 (flat rate)
3 x Product 2 (flat rate)
what is my shipping?