Odd results when performing a TSE sequence

[ZemaTimoteo]

I am implementing on matlab an EPG but I encountered some mismatch when generating a TSE sequence.

I download this repousitory, and implemented a TSE similar to the example given, allowing it for an automatic design for any number of echoes.

Here is the input I am using:

%% Simulate double spin echoes with EPG
% -------------------- Tissues in (ms) -----------------------------
T1_GM = 1300;
T2_GM = 180;

% -------------------- initial parameters ---------------------------
seq.TE       = 50;                          % TE ms
seq.FA       = 170;                          % Flip angle ->20º

nechos       = 20;
seq.events   = [];
seq.time     = [];
event        = {'relax', 'rf','grad','relax'};
Tstart_event = [0 seq.TE/2];
Gstart_event = [1];
seq.events   = {'rf','grad'};
seq.time     = Tstart_event;
seq.grad     = [Gstart_event];

phi      = [90 zeros(1,nechos)];       % CPMG 
FA       = [90 ones(1,nechos)*seq.FA]; % FA for GM in the start
seq.rf  = [phi; FA];

for neco = 1:nechos
    seq.events = [seq.events , event];                              % Sequence of events
    seq.time   = [seq.time   , seq.TE*neco-seq.TE/2, seq.TE*neco-seq.TE/2, seq.TE*neco, seq.TE*neco];   % Time in ms
    seq.grad   = [seq.grad, 1];
end
seq.T1     = T1_GM;
seq.T2     = T2_GM;

% ------------------- Get EPG ----------------------------------
% IMR - Framework EPG
[om_store,echoes] = EPG_custom(seq); 

For a Flip Angle (FA) of 180º , I get a well behaviour and expected plot Fig1. However, if I vary the FA the behaviour seems to be unexpected. Specially, when considering up and down oscilations for the Intensity of the signal. Fig2 (FA=170) or Fig3 (FA=30)

Could you please let me know what am I doing wrong, and how can I overcome this issue?

Best
Tiago

Fig1. FA = 180º

Fig2. FA = 170º

Fig3. FA = 30º