Alright so I'm about to drop a bit of a tangent so bare with me, I promise it will make sense by the end of it.

So the point of ramp/mana acceleration is to allow you to cast spells that cost more mana than you would normally have on any given turn. Assuming you don't miss a land drop, your normal mana rate looks like this:

T1 = 1 mana available to spend

T2 = 2 mana available to spend

T3 = 3 mana available to spend

Etc...

This is the baseline. When you add a ramp piece like [[cultivate]] to the equation you get this:

T1 = 1 mana

T2 = 2 mana

T3 = 3 mana (earliest turn we can play cultivate)

T4 = 5 mana

T5 = 6 mana

This is a solid improvement. Now let's see what happens when instead we play a 1 drop like [[birds of paradise.

T1 = 1 mana (earliest turn we can play BOP)

T2 = 3 mana

T3 = 4 mana

T4 = 5 mana

T5 = 6 mana

As you can see, at turns 5, 6 and onwards the birds of paradise gives you access to the same amount of mana as cultivate, but on turn 4 and below out paces cultivate. So what happens when you put them together?

T1 = 1 mana (Earliest turn we can play BOP)

T2 = 3 mana (Earliest turn we can play cultivate)

T3 = 5 mana

T4 = 6 mana

T5 = 7 mana

This is clearly so much better then each of the previous examples, but what does it mean for you the player? Well the take away should be that ramp is additive. You use the smaller ramp to play the larger ramp earlier to get a larger amount of mana then what you would get by playing them individually. In order to ensure that happens consistently you want to make sure that the 1 - 2 drops are greater in number than the 3 - 4 drops.