Winning government work (which is probably similar to large enterprise) is all about ensuring all of the government tender requirements get a "yes" tick when considering your product, but then ensuring that your fine print gets you out of all the unsavory things you had to agree to for those "yes" ticks. You can afford at this stage of the process to underprice and beat your competition. Note that the thing you underprice is the fixed price commitments that the government will change anyway, invalidating your fix price commitment instead switching over to the overpriced fine print pricing (see below).
You might wonder how to do that without them noticing that you are backing out of all your commitments. You in effect force them to agree that the fixed price commitments that you make are only valid if the government does their bit of the project, and you lock down exactly what their bit is. Anything outside this clearly defined scope is a "variation" or "change".
You do it by identifying the grey areas and putting a condition on each grey area.
For example there might be a requirement in the tender that you'll deliver some report in a week, or build some software function in 3 months at a fixed price. You would have some fine print to say "if all client staff are available to contribute, if all systems are fully available for review and if all approvals are gained. 1 week project $2,000 additional hours $220 per hour". You know its going to take far more than one week, now you are going to get paid for it, but you charged only $2,000 for the initial week which was likely cheaper than the other tender submitting companies who you are competing with. You just got them to agree to pay you $220/hour, and they didn't realize that most of the project will actually be carried out under this bit of fine print because they didn't meet their commitment to their side of the project - bingo!
Your client can't disagree with the grey area conditions because its only reasonable that if they require the report in a week that they do their side of the project work and if they don't then you need to be paid for the extra time it is taking.
Your client will be optimistic about what they can do when it comes to what they need to contribute to the project. Take advantage of that optimism and get them to be paying you when it takes them longer than they expected to do their bit.
The real money is made in these additional terms because in many cases all the initial conditions of the contract become irrelevant for various reasons and thus the terms are dictated by the fine print that you defined, that the client is not paying close attention to during the tender assessment process because all they care about is ticking off their predefined requirements, which you already made sure you get a big "yes" tick on. This is how big companies make scads of money from government consulting contracts. They know to make their initial tender extremely appealing to the client and their fine print extremely lucrative.
Make sure you have a good project manager whose job is mainly to track actual against contract commitments and get signoff when moving to hourly instead of the fixed price commitments.