I assume you are talking about HT and not music. Your preamp should give you options like individual speaker volume and delay to help with this.
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Agree with Zd542 that if this is for HT and you'll be using a SSP I wouldn't think this will be much of an issue. Soundstage width will likely be more a function of the quality of your L/R speakers and the upstream electronics than the placement of the center. If music is also a priority I'd consider getting a good SSP with the latest Audessey room correction to help everything blend more seamlessly. Best of luck.
The common misconception when looking at LCR diagrams is that the C speaker is recessed more. Technically, they are all supposed to be the same distance from the listening seat. When that's not possible, you compensate in your HT pre-pro and set the actual distances in the pre-pro or receiver. That unit then puts in the proper delay to address any issues related to timing.
Most entry-level pre-pros only go in 1 foot increments and higher end ones go in 1/2 foot increments. That's a generalization, of course, but something to keep in mind.