I'm a bit confused about these two options. I'm not sure if they mean exactly the same or if I should prefer the former or the latter.
Example sentence:
She had some space in front and behind her, so (that) if she spun ninety degrees in any direction, we would stop making physical contact.
I tried checking an example phrase on Google Books. But both options yield more or less the same number of results: so if she moved and so that if she moved.
I would like some insights on this.
These two phrases have similar, but nonetheless distinct, meanings.
So that if - this phrase is used when you are telling someone the purpose, reason or intent for which something has been done. In your sentence the use of so that if would imply that the space in front and behind her had been deliberately left free for the purpose of allowing her to turn ninety degrees in any direction to avoid making physical contact.
So if - this phrase is used to tell you the effect of something that has been done. In your sentence the use of so if would imply that the the result of having space in front and behind her was that it allowed her to turn ninety degrees in any direction without making physical contact. In this case there is no implication that this result was pre-planned, the result may have just been fortuitous.
If is not essential to these phrases, although it is essential in your sentence. For example:
I went to Melbourne so that I could go to the concert.
In other words, going to the concert was the reason or purpose for me travelling to Melbourne.
I am in Melbourne, so I can go to the concert.
In other words one of the effects of me being in Melbourne is that I can go to the concert, but that was not necessarily the reason for me travelling to Melbourne.
They have essentially the same meaning but a slight difference in register. so if is conversational/informal; so that if would be preferred in writing that seeks a more formal tone.
We're running out of widgets pretty fast, so if you want one you'd better buy it now.
We have modified our website to accept back-orders, so that if you would like to add your name to the waiting list, you may do so.
Try replacing 'so if' and 'so that if' with 'when' or 'so when', can read better in many instances.
