I am trying to replicate the results in Consistent Pricing of FX Options, A. Castagna and F. Mercurio. However, when I calculate the strike prices for 25-delta put and call and ATM I cannot get the same result as in the article.

The parameters given in the article (p.5):

 - T      = 94/365
 - S      = 1.205
 - s(ATM) = 0.0905
 - s(RR)  = -0.0050
 - s(BF)  = 0.0013

These result in s(25dPut) = 0.0943 and s(25dCall) = 0.0893 (equations 4 and 5 on pages 2 and 3).

 - K(25dPut)  = 1.1733
 - K(25dCall) = 1.2487

The values I get (equations 6 and 7 on p. 3) are:

 - K(25dPut)  = 1.16688287...
 - K(25dCall) = 1.2421907...

Here is my Python code:

    S       = 1.205
    tau     = 94.0 / 365.0
    iv_v    = 0.0905
    rr_v    = -0.005
    bf_v    = 0.0013
    for_df  = 0.9902752
    dom_df  = 0.9945049
    
    vol_call = iv_v + bf_v + 0.5 * rr_v
    vol_put = iv_v + bf_v - 0.5 * rr_v
    
    alpha = - scipy.stats.norm.ppf( 0.25 * np.exp( (for_df**(-1) - 1) * tau) )
    k1 = S * np.exp( - alpha * vol_put * np.sqrt(tau) + ((dom_df**(-1) - 1) - (for_df**(-1) - 1) + 0.5 * vol_put**(2) ) * tau )
    k2 = S * np.exp( alpha * vol_call * np.sqrt(tau) + ((dom_df**(-1) - 1) - (for_df**(-1) - 1) + 0.5 * vol_call**(2) ) * tau )

This code gives wrong results, but I cannot figure out where the error is.